The present invention relates to a polypeptide which possesses uracil phosphoribosyl transferase (UPRTase) activity and which is derived from a native UPRTase by one or more residues of said UPRTase being mutated. The invention also relates to a nucleotide sequence which encodes this mutant UPRTase, to a vector for expressing this latter mutant, to a viral particle and a host cell, and to a composition which comprises them. Finally, the invention is also directed towards their therapeutic use and to a method of treatment which implements them. The present invention is particularly useful, within the context of suicide gene therapy, for an application with respect, in particular, to proliferative and infectious diseases.
Gene therapy is defined as being the transfer of genetic information into a host cell or organism. The first protocol applied to man was initiated in the United States, in September 1990, on a patient who was genetically immunodeficient on account of a mutation which affected the gene encoding Adenine Deaminase (ADA). The relative success of this first experiment encouraged the development of this approach for a variety of diseases, including both genetic diseases (with the aim of correcting the malfunction of a defective gene) and acquired diseases (cancers, infectious diseases, such as AIDS, etc.). This technology has experienced a large number of developments since then, including xe2x80x9csuicide genexe2x80x9d therapy, which uses genes whose expression products are able to transform an inactive substance (prodrug) into a cytotoxic substance, thereby giving rise to cell death. In 1992, several groups demonstrated the relevance of this novel approach for treating tumors and inhibiting dissemination of the HIV virus, which is responsible for AIDS.
In this respect, the gene encoding the herpes simplex type 1 virus thymidine kinase (HSV-1 TK) constitutes the prototype of the suicide genes (Caruso et al., 1993, Proc. Natl. Acad. Sci. USA 90, 7024-7028; Culver et al., 1992, Science 256, 1550-1552; Ram et al., 1997, Nat. Med. 3, 1354-1361). While the TK polypeptide is not toxic as such, it catalyzes the transformation of nucleoside analogues such as acyclovir or ganciclovir (GCV). The modified nucleosides are incorporated into the DNA chains which are in the process of elongation, inhibiting cell division as a consequence. A large number of suicide gene/prodrug pairs are currently available. Those which may more specifically be mentioned are rat cytochrome p450 and cyclophosphophamide [sic] (Wei et al., 1994, Human Gene Therapy 5, 969-978), Escherichia coli (E. Coli) purine nucleoside phosphorylase and 6-methylpurine deoxyribonucleoside (Sorscher et al., 1994, Gene Therapy 1, 223-238), E. coli guanine phosphoribosyl transferase and 6-thioxanthine (Mzoz and Moolten, 1993, Human Gene Therapy 4, 589-595) and cytosine deaminase (CDase) and 5-fluorocytosine (5FC).
CDase is involved in the pyrimidine metabolic pathway by which exogenous cytosine is transformed into uracil by means of a hydrolytic deamination. While CDase activities have been demonstrated in prokaryotes and lower eukaryotes (Jund and Lacroute, 1970, J. Bacteriol. 102, 607-615; Beck et al., 1972, J. Bacteriol. 110, 219-228; De Haan et al., 1972, Antonie van Leeuwenhoek 38, 257-263; Hoeprich et al., 1974, J. Inf. Dis. 130, 112-118; Esders and Lynn, 1985, J. Biol. Chem. 260, 3915-3922), they are not present in mammals (Koechlin et al., 1966, Biochem Pharmacol. 15, 435-446; Polak et al., 1976, Chemotherapy 22, 137-153). The Saccharomyces cerevisiae (S. cerevisiae) FCY1 and the E. coli codA genes, which respectively encode the CDase of these two organisms, are known and their sequences have been published (EP 402 108; Erbs et al., 1997, Curr. Genet. 31, 1-6; WO93/01281).
CDase also deaminates an analogue of cytosine, i.e. 5-fluorocytosine (5-FC), thereby forming 5-fluorouracil (5-FU), which is a compound which is highly cytotoxic when it is converted into 5-fluoro-UMP (5-FUMP). Cells which lack CDase activity, either because of a mutation which inactivates the gene encoding the enzyme or because they are naturally deficient in this enzyme, as are mammalian cells, are resistant to 5-FC (Jund and Lacroute, 1970, J. Bacteriol, 102, 607-615; Kilstrup et al., 1989, J. Bacteriol. 1989 171, 2124-2127). By contrast, mammalian cells into which the sequences encoding CDase activity were transferred became sensitive to 5-FC (Huber et al., 1993, Cancer Res. 53, 4619-4626; Mullen et al., 1992, Proc. Natl. Acad. Sci. USA 89, 33-37; WO 93/01281). In addition, the neighboring, untransformed cells also become sensitive to 5-FC (Huber et al., 1994, Proc. Natl. Acad. Sci. USA 91, 8302-8306). This phenomenon, which is termed a bystander effect, is due to the cells which are expressing the CDase activity secreting 5-FU, which then intoxicates the neighboring cells by straightforward diffusion across the plasma membrane. This property of 5-FU in diffusing passively represents an advantage as compared with the tk/GCV reference system, where the bystander effect requires there to be contact with the cells which are expressing tk (Mesnil et al., 1996, Proc. Natl. Acad. Sci. USA 93, 1831-1835). All the advantages which CDase offers within the context of gene therapy, in particular anticancer gene therapy, can therefore be readily understood.
However, the sensitivity to 5-FC varies a great deal depending on the cell lines employed. For example, a low degree of sensitivity is observed in human tumor cell lines PANC-1 (pancreatic carcinoma) and SK-BR-3 (breast adenocarcinoma) which have been transduced with a retrovirus expressing the E. coli coda gene (Harris et al., 1994, Gene Therapy 1, 170-175). This undesirable phenomenon could be explained by the 5-FU which is formed by the enzymic action of the CDase either not being converted, or only being converted at a low level, into cytotoxic 5-FUMP. This step, which is normally effected in mammalian cells by orotate phosphorybosyl [sic] transferase (Peters et al., 1991, Cancer 68, 1903-1909), may be absent in particular tumors and thereby render the CDase-based gene therapy inoperative.
In prokaryotes and lower eukaryotes, uracil is transformed into UMP by the action of uracil phosphoribosyl transferase (UPRTase). This enzyme also converts 5-FU into 5-FUMP. Thus, furl mutants of the yeast S. cerevisiae are resistant to high concentrations of 5-FU (10 mM) and 5-FC (10 mM) because, with there being no UPRTase activity, the 5-FU which arises from the deamination of the 5-FC by CDase is not transformed into cytotoxic 5-FUMP (Jund and Lacroute, 1970, J. Bacteriol. 102, 607-615). The upp and FUR1 genes, which encode E. coli and S. cerevisiae UPRTase, respectively, have been cloned and sequenced (Andersen et al., 1992, Eur. J. Biochem. 204, 51-56; Kern et al., 1990, Gene 88, 149-157).
In order to remedy these drawbacks, the prior art document WO-A-96/16183 recommends using a fusion protein which encodes a two-domain enzyme possessing CDase and UPRTase activities, and demonstrates in vitro that the transfer of a hybrid codA::upp or FCY1::FUR1 gene, carried by an expression plasmid, increases the sensitization of transfected B16 cells to 5-FC.
The present invention is an improvement of the earlier technique in that it uses a mutated FUR1 gene which encodes a UPRTase which is deleted in its N-terminal part. The present invention results from the observation that, after the initiating ATG codon, the FUR1 gene contains a second ATG codon encoding methionine in position 36 of the native protein.
An FUR1 gene has now been constructed which lacks 105 nucleotides at the 5xe2x80x2 end of the coding part, thereby making it possible to synthesize a UPRTase from which the first 35 N-terminal residues have been deleted and which starts with the methionine in position 36 in the native protein. It has been shown that the expression product of the mutant gene, designated FUR1xcex94105, is able to complement an S. cerevisiae furl mutant, thereby demonstrating that it is functional. Surprisingly, the truncated mutant exhibits a UPRTase activity which is greater than that of the native enzyme, as is testified by the enzyme assays which have been carried out on COS7 cells transfected with a plasmid expressing the corresponding gene (FUR1xcex94105 gene as compared with the wild-type gene). Three human tumor cell lines, which were selected because of their resistance to 5-FU, were transduced with the mutant gene carried by an adenoviral vector and exhibit an increased sensitivity to 5-FU in vitro. The sensitivity to 5-FC is also increased if the cells are coinfected with adenoviruses which are respectively expressing the FCY1 and FUR1xcex94105 genes, as compared with an infection with an adenovirus expressing FCY1 alone. Even more surprisingly, the fusion protein which is produced by the hybrid FCY1::FU1xcex94105 gene, which results from the in-frame fusion of the FCY1 and truncated FUR1 genes, retains its UPRTase activity but exhibits a CDase activity which is increased by a factor of 10 to 30 as compared with that measured using the native FCY1 product. The high CDase activity of the bifunctional protein makes it possible to form a pool of 5-FU which generates a substantial bystander effect. It is to be noted that the CDase activity of the CDase::UPRTase fusion protein of WO-A-96/16183 was not shown to be improved.
The present invention provides a more efficient mutant, thereby making it possible to increase the sensitivity of cells to 5-FC and to improve the prospects for gene therapy using suicide genes. This mutant can be used for a large number of applications, in particular anticancer and antiviral applications, and all applications which require cell death.
For this reason, the present invention relates to a polypeptide possessing a uracil phosphoribosyl transferase (UPRTase) activity, characterized in that it is derived from a native UPRTase at least by mutating one or more residues of said UPRTase.
Within the meaning of the present invention, a polypeptide possessing a UPRTase activity refers to a polypeptide which is able to convert uracil, or one of its derivatives, into a monophosphate analog, in particular 5-FU into 5-FUMP. xe2x80x9cMutationxe2x80x9d is to be understood as being the addition, deletion and/or substitution of one or more residues at any site in said polypeptide.
The native UPRTase from which the polypeptide according to the invention is derived can be of any origin, in particular of prokaryotic, fungal or yeast origin. By way of illustration, the UPRTases from E. coli (Anderson et al., 1992, Eur. J. Biochem 204, 51-56), from Lactococcus lactis (Martinussen and Hammer, 1994, J. Bacteriol. 176, 6457-6463), from Mycobacterium bovis (Kim et al., 1997, Biochem Mol. Biol. Int 41, 1117-1124) and from Bacillus subtilis (Martinussen et al., 1995, J. Bacteriol. 177, 271-274), can be used within the context of the invention. However, very particular preference is given to using a yeast UPRTase, in particular that encoded by the S. cerevisiae FUR1 gene, whose sequence is disclosed in Kern et al. (1990, Gene 88, 149-157). By way of information, the sequences of the genes, and those of the corresponding UPRTases, can be found in the literature and in specialized databases (SWISSPROT, EMBL, Genbank, Medline, etc.).
According to one particularly advantageous embodiment, the polypeptide according to the invention is a deletion mutant of a native UPRTase. The deletion is preferably located in the N-terminal region of the original UPRTase. The deletion can be total (affecting all the residues of said N-terminal region) or partial (affecting one or more residues which may or may not be continuous in the primary structure). In a general manner, a polypeptide consists of an N-terminal part, of a central part and of a C-terminal part, with each part representing approximately one third of the molecule. For example, in the case of the S. cerevisiae UPRTase, which contains 251 amino acids, the N-terminal part consists of the first 83 residues, starting with the so-called initiating methionine, which is located in the first position of the native form. In the case of the E. coli UPRTase, the N-terminal part covers positions 1 to 69.
This preferred embodiment can of course be combined with one or more additional mutation(s) at any site in the molecule. Preferably, the additional modification(s) do not significantly affect the UPRTase enzymic properties of the polypeptide according to the invention. It is pointed out that the biological activity of the mutants can be tested, in particular using the techniques which are described in the examples which follow.
Very preferably, the polypeptide according to the invention is derived from a native UPRTase at least by deleting all or part of the N-terminal region upstream of the second ATG codon of said native UPRTase. The total deletion of the aforesaid region is preferred. For example, the UPRTase encoded by the FUR1 gene comprises a first ATG codon (initiating ATG codon) in position +1 followed by a second in position +36. Thus, it is possible to envisage deleting residues +1 to 35 within the context of the present invention, thereby giving a polypeptide which starts at the methionine which is normally found in position +36 of the native form.
A preferred polypeptide according to the invention comprises an amino acid sequence which is substantially as depicted in the SID NO: 1 sequence identifier, starting at the Met residue in position 1 and finishing at the Val residue in position 216. The term xe2x80x9csubstantiallyxe2x80x9d refers to a degree of identity with said SID NO: 1 sequence which is greater than 70%, advantageously greater than 80%, preferably greater than 90% and, very preferably greater than 95%. Still more preferably, the polypeptide comprises the amino acid sequence depicted in the SID NO: 1 sequence identifier. As mentioned above, it can contain additional mutations. Substitution of the serine residue at position 2 (position 37 in the native UPRTase) with an alanine residue may in particular be mentioned.
Advantageously, the polypeptide according to the invention exhibits a UPRTase activity which is appreciably higher than that exhibited by said native UPRTase. The results which are presented in the examples which follow clearly demonstrate a more rapid and/more efficient conversion of 5-FU into 5-FUMP, manifesting itself in a higher degree of cytotoxicity with regard to the transfected or transduced cells. Advantageously, the UPRTase activity of the polypeptide according to the invention is greater than that exhibited by the native UPRTase by a factor of from 2 to 100, preferably of from 5 to 75, and very preferably of from 10 to 50.
According to another embodiment, the polypeptide according to the invention is a fusion polypeptide in which it is fused in-frame with at least one second polypeptide. Even though the fusion can take place at any site in the first polypeptide, the N- or C-terminal ends are preferred, in particular the N-terminal end. Advantageously, the in-frame fusion uses a second polypeptide which exhibits a cytosine deaminase (CDase) activity and is derived from a native cytosine deaminase, such that the fusion polypeptide according to the invention exhibits CDase and UPRTase activities. An FCY1::FUR1 fusion (designated FCU1 below) is preferred. Such a bifunctional polypeptide makes it possible to improve the sensitivity of the target cells to 5-FC and 5-FU. xe2x80x9cCytosine deaminase activityxe2x80x9d is understood as covering the deamination of cytosine or one of its analogs. Preferably, the second polypeptide according to the invention is able to metabolize 5-FC into 5-FU.
A CDase of prokaryotic or lower eukaryotic origin is used within the context of the present invention. Still more preferably, the CDase is a yeast CDase, in particular that encoded by the Saccharomyces cerevisiae FCY1 gene. The cloning and the sequence of the genes encoding the CDases of different origins are available in the literature and the specialized databases. For information, the sequence of the FCY1 gene is disclosed in Erbs et al. (1997, Curr. Genet. 31, 1-6). It is of course possible to use a CDase mutant which possesses a conversion ability which is comparable or superior to that of the native enzyme. The skilled person is capable of cloning the CDase sequences on the basis of the published data, of carrying out any mutations, of testing the enzymic activity of the mutant forms in an acellular or cellular system in accordance with the technique of the art, or following the protocol given below, and of fusing the polypeptides having CDase and UPRTase activity in-frame.
A preferred example is a polypeptide which comprises an amino acid sequence which is substantially as depicted in the SID NO: 2 sequence identifier, starting at the Met residue in position 1 and finishing at the Val residue in position 373. The term xe2x80x9csubstantiallyxe2x80x9d is defined as before. A polypeptide which comprises the amino acid sequence as depicted in the SID NO: 2 sequence identifier is very particularly appropriate for implementing the invention.
According to an advantageous embodiment, a bifunctional polypeptide according to the invention exhibits a CDase activity which is appreciably higher than that of said native CDase. Thus, the examples which follow demonstrate that coupling the two enzymes makes it possible to increase the sensitization of the target cells to 5-FC. The factor by which the sensitization is increased is advantageously at least 2, preferably at least 5 and, very preferably, 10 or more.
In a general manner, a polypeptide according to the invention can be produced either by the conventional methods of chemical synthesis or by recombinant DNA techniques (see, for example, Maniatis et al., 1989, Laboratory Manual, Cold Spring Harbor, Laboratory Press, Cold Spring Harbor, N.Y.). For this reason, the present invention also covers a preparation process in which a nucleotide sequence encoding said polypeptide is introduced into a cell in order to generate a transformed cell, said transformed cell is cultured under conditions appropriate for enabling said polypeptide to be produced, and said polypeptide is harvested from the cell culture. The producer cell can be of any origin and, without limitation, a bacterium, a yeast or a mammalian cell, to the extent that the nucleotide sequence under consideration is either integrated into its genome or integrated into an appropriate expression vector which is able to replicate. Naturally, the nucleotide sequence is placed under the control of transcription and translation signals which enable it to be expressed in the producer cell. Expression vectors and control signals are known to the skilled person. The polypeptide can be recovered from the medium or the cells (after they have been lyzed) and subjected to conventional purification steps (by chromatography, electrophoresis, filtration, immunopurification, etc.).
The present invention also relates to a nucleotide sequence which encodes a polypeptide according to the invention. The nucleotide sequence can be a cDNA or genomic sequence or be of a mixed type. It can, where appropriate, contain one or more introns, with these being of native, heterologous (for example the intron of the rabbit xcex2-globin gene, etc.) or synthetic origin, in order to increase expression in the host cells. As has already been pointed out, said sequence can encode a polypeptide which is derived from the native enzyme or a mutant which exhibits a comparable or superior activity. The sequences employed within the context of the present invention can be obtained by the conventional techniques of molecular biology, for example by screening libraries with specific probes, by immunoscreening expression libraries or by PCR using suitable primers, or by chemical synthesis. The mutants can be generated from the native sequences by substituting, deleting and/or adding one or more nucleotides using the techniques of site-directed mutagenesis, of PCR, of digesting with restriction and ligation enzymes, or else by chemical synthesis. The ability of the mutants and constructs to function can be verified by assaying the enzymic activity or by measuring the sensitivity of target cells to 5-FC and/or 5-FU.
The present invention also relates to a recombinant vector which carries a nucleotide sequence according to the invention which is placed under the control of the elements which are required for expressing it in a host cell. The recombinant vector can be of plasmid or viral origin and can, where appropriate, be combined with one or more substances which improve the transfectional efficiency and/or stability of the vector. These substances are widely documented in the literature which is available to the skilled person (see, for example, Felgner et al., 1987, Proc. West. Pharmacol. Soc. 32, 115-121; Hodgson and Solaiman, 1996, Nature Biotechnology 14, 339-342; Remy et al., 1994, Bioconjugate Chemistry, 5, 647-654). By way of non-limiting illustration, the substances can be polymers, lipids, in particular cationic lipids, liposomes, nuclear proteins or neutral lipids. These substances can be used alone or in combination. A combination which can be envisaged is that of a recombinant plasmid vector which is combined with cationic lipids (DOGS, DC-CHOL, sperimine-chol, spermidine-chol, etc.) and neutral lipids (DOPE).
The choice of the plasmids which can be used within the context of the present invention is immense. They can be cloning vectors and/or expression vectors. In a general manner, they are known to the skilled person and, while a number of them are available commercially, it is also possible to construct them or to modify them using the techniques of genetic manipulation. Examples which may be mentioned are the plasmids which are derived from pBR322 (Gibco BRL), pUC (Gibco BRL), pBluescript (Stratagene), pREP4, pCEP4 (Invitrogene) or p Poly (Lathe et al., 1987, Gene 57, 193-201). Preferably, a plasmid which is used in the context of the present invention contains an origin of replication which ensures that replication is initiated in a producer cell and/or a host cell (for example, the ColE1 origin will be chosen for a plasmid which is intended to be produced in E. coli and the oriP/EBNA1 system will be chosen if it desired that the plasmid should be self-replicating in a mammalian host cell, Lupton and Levine, 1985, Mol. Cell. Biol. 5, 2533-2542; Yates et al., Nature 313, 812-815). The plasmid can additionally comprise a selection gene which enables the transfected cells to be selected or identified (complementation of an auxotrophic mutation, gene encoding resistance to an antibiotic, etc.). Naturally, the plasmid can contain additional elements which improve its maintenance and/or its stability in a given cell (cer sequence, which promotes maintenance of a plasmid in monomeric form (Summers and Sherrat, 1984, Cell 36, 1097-1103, sequences for integration into the cell genome).
With regard to a viral vector, it is possible to envisage a vector which is derived from a poxvirus (vaccinia virus, in particular MVA, canarypoxvirus, etc.), from an adenovirus, from a retrovirus, from a herpesvirus, from an alphavirus, from a foamy virus or from an adenovirus-associated virus. Preference will be given to using a vector which does not replicate and does not integrate. In this respect, adenoviral vectors are very particularly suitable for implementing the present invention.
Retroviruses have the property of infecting, and in most cases integrating into, dividing cells and in this regard are particularly appropriate for use in relation to cancer. A recombinant retrovirus according to the invention generally contains the LTR sequences, an encapsidation region and the nucleotide sequence according to the invention, which is placed under the control of the retroviral LTR or of an internal promoter such as those described below. The recombinant retrovirus can be derived from a retrovirus of any origin (murine, primate, feline, human, etc.) and in particular from the MoMuLV (Moloney murine leukemia virus), MVS (Murine sarcoma virus) or Friend murine retrovirus (Fb29). It is propagated in an encapsidation cell line which is able to supply in trans the viral polypeptides gag, pol and/or env which are required for constituting a viral particle. Such cell lines are described in the literature (PA317, Psi CRIP GP+Am-12 etc.). The retroviral vector according to the invention can contain modifications, in particular in the LTRs (replacement of the promoter region with a eukaryotic promoter) or the encapsidation region (replacement with a heterologous encapsidation region, for example the VL30 type) (see French applications 94 08300 and 97 05203).
Preference will be given to using an adenoviral vector which lacks all or part of at least one region which is essential for replication and which is selected from the E1, E2, E4 and L1-L5 regions in order to avoid the vector being propagated within the host organism or the environment. A deletion of the E1 region is preferred. However, it can be combined with (an)other modification(s)/deletion(s) affecting, in particular, all or part of the E2, E4 and/or L1-L5 regions, to the extent that the defective essential functions are complemented in trans by means of a complementing cell line and/or a helper virus. In this respect, it is possible to use second-generation vectors of the state of the art (see, for example, international applications WO-A-94/28152 and WO-A-97/04119). By way of illustration, deletion of the major part of the E1 region and of the E4 transcription unit is very particularly advantageous. For the purpose of increasing the cloning capacities, the adenoviral vector can additionally lack all or part of the non-essential E3 region. According to another alternative, it is possible to make use of a minimal adenoviral vector which retains the sequences which are essential for encapsidation, namely the 5xe2x80x2 and 3xe2x80x2 ITRs (Inverted Terminal Repeat), and the encapsidation region. The various adenoviral vectors, and the techniques for preparing them, are known (see, for example, Graham and Prevect, 1991, in Methods in Molecular Biology, Vol 7, p 109-128; Ed: E. J. Murey, The Human Press Inc).
Furthermore, the origin of the adenoviral vector according to the invention can vary both from the point of view of the species and from the point of view of the serotype. The vector can be derived from the genome of an adenovirus of human or animal (canine, avian, bovine, murine, ovine, porcine, simian, etc.) origin or from a hybrid which comprises adenoviral genome fragments of at least two different origins. More particular mention may be made of the CAV-1 or CAV-2 adenoviruses of canine origin, of the DAV adenovirus of avian origin or of the Bad type 3 adenovirus of bovine origin (Zakharchuk et al., Arch. Virol., 1993, 128: 171-176; Spibey and Cavanagh, J. Gen. Virol. 1989, 70: 165-172; Jouvenne et al., Gene, 1987, 60: 21-28; Mittal et al., J. Gen. Virol., 1995, 76: 93-102). However, preference will be given to an adenoviral vector of human origin which is preferably derived from a serotype C adenovirus, in particular a type 2 or 5 serotype C adenovirus.
An adenoviral vector according to the present invention can be generated in vitro in Escherichia coli (E. coli) by ligation or homologous recombination (see, for example, international application WO-A-96/17070) or else by recombination in a complementing cell line.
The elements required for expression consist of all the elements which enable the nucleotide sequence to be transcribed into RNA and the mRNA to be translated into polypeptide. These elements comprise, in particular, a promoter which may be regulatable or constitutive. Naturally, the promoter is suited to the chosen vector and the host cell. Examples which may be mentioned are the eukaryotic promoters of the PGK (phosphoglycerate kinase), MT (metallothionein; McIvor et al., 1987, Mol. Cell Biol. 7, 838-848), xcex1-1 antitrypsin, CFTR, surfactant, immunoglobulin, xcex2-actin (Tabin et al., 1982, Mol. Cell Biol. 2, 426-436) and SRxcex1 (Takebe et al., 1988, Mol. Cell Biol. 8, 466-472) genes, the early promoter of the SV40 virus (Simian virus), the LTR of RSV (Rous sarcoma virus), the HSV-1 TK promoter, the early promoter of the CMV virus (Cytomegalovirus), the p7.5K pH5R, pK1L, p28 and p11 promoters of the vaccinia virus, and the E1A and MLP adenoviral promoters. The promoter can also be a promoter which stimulates expression in a tumor or cancer cell. Particular mention may be made of the promoters of the MUC-1 gene, which is overexpressed in breast and prostate cancers (Chen et al., 1995, J. Clin. Invest. 96, 2775-2782), of the CEA (standing for carcinoma embryonic antigen) gene, which is overexpressed in colon cancers (Schrewe et al., 1990, Mol. Cell. Biol. 10, 2738-2748) of the tyrosinase gene, which is overexpressed in melanomas (Vile et al., 1993, Cancer Res. 53, 3860-3864), of the ERBB-2 gene, which is overexpressed in breast and pancreatic cancers (Harris et al., 1994, Gene Therapy 1, 170-175) and of the xcex1-fetoprotein gene, which is overexpressed in liver cancers (Kanai et al., l997, Cancer Res. 57, 461-465). The cytomegalovirus (CMV) early promoter is very particularly preferred.
The necessary elements can furthermore include additional elements which improve the expression of the nucleotide sequence according to the invention or its maintenance in the host cell. Intron sequences, secretion signal sequences, nuclear localization sequences, internal sites for the reinitiation of translation of IRES type, transcription termination poly A sequences, tripartite leaders and origins of replication may in particular be mentioned. These elements are known to the skilled person.
The recombinant vector according to the invention can also comprise one or more additional genes of interest, with it being possible for these genes to be placed under the control of the same regulatory elements (polycistronic cassette) or of independent elements. Genes which may in particular be mentioned are the genes encoding interleukins IL-2, IL-4, IL-7, IL-10 and IL-12, interferons, tumor necrosis factor (TNF), colony stimulating factors (CSF), in particular GM-CSF, and factors acting on angiogenesis (for example PAI-1, standing for plasminogen activator inhibitor). In one particular embodiment, the recombinant vector according to the invention comprises the gene of interest encoding IL-2 or encoding interferon xcex3 (INFxcex3). It is also possible to envisage combining the nucleotide sequence according to the invention with other suicide genes such as the HSV-1 TK gene, the ricin gene, the cholera toxin gene, etc.
The present invention also relates to a viral particle which comprises a recombinant vector according to the invention. Such a viral particle can be generated from a viral vector using any technique which is conventional in the field of the art. The viral particle is propagated in a complementing cell which is suited to the deficiencies of the vector. With regard to an adenoviral vector, use will, for example, be made of the 293 cell line, which was established using human embryonic kidney cells and which efficiently complements the E1 function (Graham et al., 1977, J. Gen. Virol. 36, 59-72), of the A549-E1 cell line (Imler et al., 1996, Gene Therapy 3, 75-84) or of a cell line which permits double complementation (Yeh et al., 1996, J. Virol. 70, 559-565; Krougliak and Graham, 1995, Human Gene Therapy 6, 1575-1586; Wang et al., 1995 Gene Therapy 2, 775-783; international application WO 97/04119). It is also possible to employ helper viruses to at least partially complement the defective functions. A complementing cell is understood as being a cell which is able to supply in trans the early and/or late factors which are required for encapsidating the viral genome in a viral capsid in order to generate a viral particle which contains the recombinant vector. Said cell may not be able to complement all the defective functions of the vector on its own and, in this case, can be transfected/transduced with a vector/helper virus which supplies the additional functions.
The invention also relates to a process for preparing a viral particle, in which process:
(i) a recombinant vector according to the invention is introduced into a complementing cell which is able to complement said vector in trans, so as to obtain a transfected complementing cell,
(ii) said transfected complementing cell is cultured under conditions which are appropriate for enabling said viral particle to be produced, and
(iii) said viral particle is recovered from the cell culture.
While the viral particle can of course be recovered from the culture supernatant, it can also be recovered from the cells. One of the commonly employed methods consists in lysing the cells by means of consecutive freezing/thawing cycles in order to collect the virions in the lysis supernatant. The virions can then be amplified and purified using the techniques of the art (chromatographic method, method of ultra-centrifugation, in particular through a cesium chloride gradient, etc.).
The present invention also relates to a host cell which comprises a nucleotide sequence or a recombinant vector according to the invention, or is infected with a viral particle according to the invention. For the purposes of the present invention, a host cell consists of any cell which can be transfected with a recombinant vector or can be infected with a viral particle, as defined above. A mammalian cell, in particular a human cell is very particularly suitable. The cell can comprise said vector in a form which is or is not (episome) integrated into the genome. The cell can be a primary or tumor cell of any origin, in particular an hematopoietic cell (totipotent stem cell, leukocyte, lymphocyte, monocyte or macrophage, etc.), muscle cell (satellite cell, myocyte, myoblast, smooth muscle cell, etc.), cardiac cell, pulmonary cell, tracheal cell, hepatic cell, epithelial cell or fibroblast.
The present invention also relates to a composition which comprises a polypeptide, a nucleotide sequence, a recombinant vector, a viral particle or a host cell according to the invention in combination with a pharmaceutically acceptable excipient.
The present invention also relates to a composition which comprises a polypeptide according to the invention which exhibits a UPRTase activity and another polypeptide of interest, in particular a polypeptide of the prior art which exhibits a CDase activity.
The present invention furthermore relates to a composition which comprises a polypeptide according to the invention and a polypeptide of interest which is encoded by one of the previously mentioned genes of interest. Of these polypeptides of interest, particular mention may be made of interleukins IL-2, IL-4, IL-7, IL-10 and IL-12, interferons, tumor necrosis factor (TNF), colony stimulating factors (CSF), in particular GM-CSF, and factors acting on angiogenesis (for example PAI-1, standing for plasminogen activator inhibitor). IL-2 or INFxcex3 are very particularly envisaged.
The composition can also be based on nucleotide sequences which enable the above polypeptides to be expressed within the host cell. The nucleotide sequences may be carried by one and the same expression vector or by two independent vectors. Said composition can of course comprise viral particles which are generated from (a) viral vector(s) expressing said nucleotide sequence(s).
For this reason, the present invention also relates to a composition which comprises a nucleotide sequence according to the invention which encodes a polypeptide exhibiting a URPTase activity and a second nucleotide sequence of interest which encodes, in particular, a polypeptide exhibiting a CDase activity.
The present invention additionally relates to a composition which comprises a nucleotide sequence according to the invention and a second nucleotide sequence of interest which encodes a polypeptide selected from IL-2 and INFxcex3.
A composition according to the invention is more specifically intended for the preventive or curative treatment of diseases by means of gene therapy and is more specifically aimed at proliferative diseases (cancers, tumors, restenosis, etc.) and at diseases of infectious origin, in particular of viral origin (induced by hepatitis B or C viruses, HIV, herpes, retroviruses, etc.).
A composition according to the invention can be made conventionally with a view to administering it locally, parenterally or by the digestive route. In particular, a therapeutically effective quantity of the therapeutic or prophylactic agent is combined with a pharmaceutically acceptable excipient. It is possible to envisage a large number of routes of administration. Examples which may be mentioned are the intragastric, subcutaneous, intracardiac, intramuscular, intravenous, intraperitoneal, intratumor, intranasal, intrapulmonary and intratracheal routes. In the case of these three latter embodiments, it is advantageous for administration to take place by means of an aerosol or by means of instillation. The administration can take place as a single dose or as a dose which is repeated on one or more occasions after a particular time interval. The appropriate route of administration and dosage vary depending on a variety of parameters, for example the individual, the disease to be treated or the gene(s) of interest to be transferred. The preparations based on viral particles according to the invention can be formulated in the form of doses of between 104 and 1014 pfu (plaque-forming units), advantageously 105 and 1013 pfu, preferably 106 and 1012 pfu. As far as the recombinant vector according to the invention is concerned, it is possible to envisage doses comprising from 0.01 to 100 mg of DNA, preferably from 0.05 to 10 mg, very particularly preferably from 0.5 to 5 mg. A composition based on polypeptides preferably comprises from 0.05 to 10 g, very particularly preferably from 0.05 to 5 g, of said polypeptide. Naturally, the doses can be adjusted by the clinician.
The formulation can also include a diluent, an adjuvant or an excipient which is acceptable from the pharmaceutical point of view, as well as solubilizing, stabilizing and preserving agents. In the case of an injectable administration, preference is given to a formulation in an aqueous, non-aqueous or isotonic solution. It can be presented as a single dose or as a multidose, in liquid or dry (powder, lyophilizate, etc.) form which can be reconstituted at the time of use using an appropriate diluent. The formulation can also comprise appropriate quantities of prodrugs.
The present invention also relates to the therapeutic or prophylactic use of a polypeptide, of a recombinant vector, of a viral particle or of a host cell according to the invention for preparing a medicament which is intended for treating the human or animal body by gene therapy or by administering protein which has been produced by the recombinant route. According to a first possibility, the medicament can be administered directly in vivo (for example by intravenous injection, into an accessible tumor, into the lungs by means of an aerosol, into the vascular system using an appropriate catheter, etc.). It is also possible to adopt the ex vivo approach, which consists in removing cells from the patient (bone marrow stem cells, peripheral blood lymphocytes, muscle cells, etc.), transfecting or infecting them in vitro in accordance with the techniques of the art and then readministering them to the patient. A preferred use consists in treating or preventing cancers, tumors and diseases which result from unwanted cell proliferation. Conceivable applications which may be mentioned are cancers of the breast, of the uterus (in particular those induced by papilloma viruses), of the prostate, of the lung, of the bladder, of the liver, of the colon, of the pancreas, of the stomach, of the esophagus, of the larynx, of the central nervous system and of the blood (lymphomas, leukemia, etc.). It can also be used in the context of cardiovascular diseases, for example in order to inhibit or retard the proliferation of the smooth muscle cells of the blood vessel wall (restenosis). Finally, in the case of infectious diseases, it is possible to conceive of the medicament being applied to AIDS.
The invention also extends to a method for treating diseases by gene therapy, characterized in that a nucleotide sequence, a recombinant vector, a viral particle or a host cell according to the invention is administered to an host organism or cell which is in need of such treatment.
When the treatment method makes use of a nucleotide sequence, a recombinant vector or a viral particle enabling a polypeptide according to the invention, which possesses a UPRTase activity, to be expressed, it can be advantageous to additionally administer a second nucleotide sequence which encodes a second polypeptide exhibiting a CDase activity, with said second nucleotide sequence being carried by said recombinant vector or viral particle or by an independent vector or viral particle. In this latter case, the UPRTase and CDase sequences can be administered simultaneously or consecutively, with the order of administration being of no importance.
According to an advantageous embodiment, the therapeutic use or the treatment method also comprises an additional step in which pharmaceutically acceptable quantities of a prodrug, advantageously an analog of cytosine, in particular 5-FC, are administered to the host organism or cell. By way of illustration, it is possible to use a dose of from 50 to 500 mg/kg/day, with a dose of 200 mg/kg/day being preferred. Within the context of the present invention, the prodrug is administered in accordance with standard practice, with the administration taking place prior to, concomitantly with or else subsequent to the administration of the therapeutic agent according to the invention. The oral route is preferred. It is possible to administer a single dose of prodrug or doses which are repeated for a time which is sufficiently long to enable the toxic metabolite to be produced within the host organism or cell.
Furthermore, the composition or method according to the invention can be combined with one or more substances which potentiate the cytotoxic effect of the 5-FU. Mention may in particular be made of drugs which inhibit the enzymes of the pathway for the de novo biosynthesis of the pyrimidines (for example those mentioned below), drugs such as Leucovorin (Waxman et al., 1982, Eur. J. Cancer Clin. Oncol. 18, 685-692), which, in the presence of the product of the metabolism of 5-FU (5-FdUMP), increases the inhibition of thymidylate synthase, resulting in a decrease in the pool of dTMP, which is required for replication, and finally drugs such as methotrexate (Cadman et al., 1979, Science 250, 1135-1137) which, by inhibiting dihydrofolate reductase and increasing the pool of PRPP (phosphoribosylpyrophosphate), brings about an increase in the incorporation of 5-FU into the cellular RNA.
The present invention is also directed towards using the sequences or recombinant vectors according to the invention as positive selection markers in mammalian cells. Advantageously, the cells are transfected and the cell mixture is then cultured in the presence of inhibitors of the pathway for the de novo biosynthesis of pyrimidines, such as PALA (N-(phosphonoacetyl)-L-aspartate; Moore et al., 1982, Biochem. Pharmacol. 31, 3317-3321), A77 1726 (active metabolite of Leflunomide; Davis et al., 1996, Biochem. 35, 1270-1273) and Brequinar (Chen et al., 1992, Cancer Res. 52, 3251-3257). The presence of such inhibitors blocks the de novo synthesis of UMP, which is required for synthesizing RNA and DNA, thereby resulting in cell death. This cytotoxic effect can be circumvented by expressing the nucleotide sequence according to the invention encoding a UPRTase activity in the presence of uracil or by coexpressing this latter sequence with sequences encoding a CDase activity (where appropriate in fused form) in the presence of cytosine. As a consequence, only the transfected cells (cells which have incorporated the UPRTase/CDase sequences) will be able to grow in the presence of inhibitors of the pyrimidine synthesis pathway. Thus, the use according to the invention enables a transfected cell to be efficiently identified in, and/or isolated from, a cell mixture.
The present invention also relates to the use of the sequences or recombinant vectors according to the invention as negative selection markers in experiments in which the genes of embryonic stem cells, on which methods for preparing transgenic animals are based, are interrupted (knocked out) (see, for example, Capecchi, 1989, Science 244, 1288-1292; Reid et al., 1990, Proc. Natl. Acad. Sci. USA 87, 4299-4303). Such a use, in combination with the gene for resistance to neomycin, for example, can make it possible to select the cells which have undergone an homologous recombination event and which will alone be able to grow in the presence of Geneticin and the corresponding fluorinated pyrimidines (5-FU if a nucleotide sequence according to the invention is used which encodes a UPRTase activity, and 5-FC when a nucleotide sequence encoding a CDase activity is also used). The cells which have undergone a non-targeted recombination event are able to grow in the presence of Geneticin but not in the presence of the fluorinated pyrimidines. Another potential use as a negative selection marker is to be found in the plant field since, just like mammalian cells, plants do not possess any endogenous CDase activity. They can be sensitized to 5-FC by transfecting a nucleotide sequence according to the invention which enables an exogenous CDase to be expressed (see, for example, Perera et al. 1993, Plant. Mol. Biol. 23, 797-799).